1. Field of the Invention
The present invention relates to a cooling unit using a thermoelectric conversion device that conducts cooling and heating based on Peltier effect and heat power generation based on Seebeck effect.
2. Description of the Related Art
In general, the thermoelectric conversion device is structured in such a manner that a p-type thermoelectric material chip and an n-type thermoelectric material chip are interposed between two substrates, and the p-type thermoelectric material chip and the n-type thermoelectric material chip which are formed on the substrates are joined to each other through a conductive material such as metal in the form of a p-n junction.
Up to now, the thermoelectric conversion device thus structured has, through the application of electricity, a function of adjusting a temperature by cooling or heating one of those substrates and a function of generating a power by differentiating the temperatures of those two substrates. To achieve those functions, it is necessary to detect and control the temperatures of those two substrates. However, a temperature sensor such as a thermistor is mounted on the substrates by adhesion or the like, and input/output electrodes of a temperature sensor and a drive terminal of the thermoelectric conversion device are connected to an external control unit and the like through a lead wire, etc.
Also, in the case where the thermoelectric conversion device is equipped with a control circuit, the thermoelectric conversion device is connected to an external control circuit through a lead wire or the like. Accordingly, the output of the temperature sensor and the drive current of the thermoelectric conversion device are matched with the control circuit after all of the temperature sensor, the control circuit and so on are mounted on and connected to the thermoelectric conversion device.
As described above, the conventional thermoelectric conversion device is required to mount the temperature sensor such as the thermistor on the substrate in order to achieve precise temperature detection or temperature control. For that reason, it is necessary to provide a region on which the temperature sensor is mounted on the substrate of the thermoelectric conversion device, and also to take account of the influence of a heat capacity of the temperature sensor. Thus, there arises such a problem that the capability beyond the performance as originally required is necessary for the thermoelectric conversion device.
Furthermore, in case of employing the thermoelectric conversion device as a cooling unit, it is general that the input/output electrodes of the thermoelectric conversion device is attached to a heat radiation sided substrate so as to prevent the load of cooling. On the other hand, it is general that the temperature sensor such as the thermistor is mounted on the cooling sided substrate. This case leads to such a problem that a heat flows into the cooling unit from the external through a lead wire connecting the temperature sensor and the external control unit, to thereby increase the load on cooling.
Also, because a three-dimensional structure is applied to the cooling unit, there arises such a problem that an increase in the costs and a deterioration of the yield are induced by the complicated structure even in a so-called packaging process in which the temperature sensor and the external control unit are connected.
Further, in order to connect the control circuit to the cooling unit for adjusting the temperature, the thermoelectric conversion device, the temperature sensor and the control circuit are required to be matched with each other. This leads to such a problem that it takes time to conduct trimming because they are different devices.
Still further, in order to provide a target temperature in the control circuit, the supply of electricity to the thermoelectric conversion device is switchingly controlled. However, the semiconductor laser used for communication suffers from such a problem that switching noises in control of the thermoelectric conversion device adversely affect the communication.
The above-mentioned problems are remarkable particularly in the small-sized thermoelectric conversion device. For example, the semiconductor laser to be used for optical communications must be cooled by the thermoelectric conversion device because the of its heating. However, since the thermoelectric conversion device to be used is so small in size such as several mm in square. Therefore, if a temperature sensor, etc. are mounted on the semiconductor laser, the cooling performance is largely adversely affected by the temperature sensor, etc., thereby resulting in problems relating to the downsizing and power consumption as the while. Further, although the thermoelectric conversion device is small in size, that is, several mm square, a large space is required for connecting the control circuit, etc., resulting in a problem that there is no scale merit.